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magnifier vs. classic tc (magnifier modeling)




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From:  FutureT [SMTP:FutureT-at-aol-dot-com]
Sent:  Friday, March 20, 1998 7:17 PM
To:  tesla-at-pupman-dot-com
Subject:  Re: magnifier vs. classic tc (magnifier modeling)

 Antonio, Bert, Malcolm, all,
 
 Corrected tests:
 
It turns out that some of my meters, etc, were inaccurate and that 
the driver coupling was lower than I previously reported, for instance
the k = .51 driver was actually k = .4.  This changes the degree of
variation between the driver and the effective coupling, but not the
general concept.  I've made corrections in the data below.

The bottom line it seems, is that a magnifier's effective coupling can
be either loose or tight (using a tightly coupled driver), depending on
the ratio of inductances between the driver and extra coil.  But the
effective coupling will always be lower than the driver coupling.

New data:

     Classic TC                                Magnifier
     ----------------                                --------------
        k = .13                                      k = .40
                                           effective  k = .18
   beat period ~ 12.5uS          beat period ~  11uS
    quench -- poor                   quench -- poor
        (3rd -- 4th notch)               (3rd -- 4th notch)
  spark,  3 1/2"  max               spark,  3 1/2"  max
 
Note in the classic TC case above, the k value does not match the
expected beat period.  The beat period shown suggests a coupling
of k = .155, so it is possible that my coupling measurement is still
not precise.  The difference in the effective k and the driver coupling
in the magnifier can be seen however.  I seem to remember Bert H
suggesting about a year ago that losses may cause the beat period
to be about 15% shorter than calculated (let me know Bert if I'm 
wrong about what you said).  This might explain the short beat
period in the classic coil?  Whatever the reason for the shorter than
expected beat period, it may suggest that the magnifier effective k
values are also somewhat lower than shown.

 Next, a secondary with a higher inductance of 5.75mH (but of the 
 same physical dimensions as the 1.5mH sec), was installed, to
 verify that the effective coupling would increase as the secondary and 
 extra coil inductances became more similar.  Tests were done using
 the 11.2mH extra coil, and also using a 21.8mH extra coil (note
 corrected values). 

     Driver k            Effective k (meas)    (calc)     Lr/Ls      Quench
                                     (extra coil)
 
   .40  (1.5mH)           .18  (11.2mH)         .14      7.5       4th notch  
 
   .33  (5.75mH)          .20  (21.8mH)         .15      3.8       5th notch

   .44  (5.75mH)          .26   (21.8mH)         .2       3.8          
 
   .33  (5.75mH)          .29   (11.2mH)        .19      1.95      6th notch
  
 It can be seen in the table above that as the ratio of
 inductance between driver and extra coil decreases, the driver k
 and the effective k become more similar.  Effective k values were
 measured by observation of the beat period relative to Fo. 
 
 There may still be some measurement inaccuracies floating about,
 but the general trend should be pretty close now.  Perhaps others
 will do similar tests to compare/verify findings.  

  John Freau